This invention pertains to breeder reactors and more particularly to breeder reactors having an orificing system flow coupled with the breeder region of same.
Breeder reactors, and more particularly fast breeder reactors, use fuel bearing radial blankets surrounding the core, for generating new fuel. The so-called breeder region (i.e., the blanket) is characterized by a predominance of fertile as opposed to fissile fuel at the beginning of core life. The energy liberated as heat in the blanket is a small varying fraction of that generated in the fissile core. Thus, the required rate of coolant flow through the radial blanket assemblies is only a fraction of that needed for cooling the core adequately.
Certain breeder reactors dealt with the differential heat production in the fertile versus the fissile region of the nuclear reactor by providing a completely separate coolant inlet structure for the breeder region. Other solutions to this problem relied upon sizing the inlet or outlet orifices in the breeder region so as to allow only a small amount of flow into the breeder region. The breeder region was generally surrounded by heavy annular walls to prevent cross-flow of coolant in the breeder region with the coolant flow in the fissile core. Still other schemes used variable outlet orifices on the breeder region so that the amount of flow therethrough could be varied and generally maintained at a small fraction of that proceeding through the fissile core of the nuclear reactor.
The above coolant flow distribution schemes also generally included canned fuel assemblies, that is, fuel assemblies which were surrounded by a relatively heavy shroud or can, so as to form discrete coolant flow channels. Such channels are generally necessary to make an orificed annular blanket region scheme operate properly.
The above-mentioned solutions generally produce a high pressure and temperature gradient across the blanket and especially at the interface of the blanket with the power producing core. The steep gradients at the interface has necessitated the use of a heavy wall structure to separate the blanket from the core. This structure was expensive, difficult to fabricate and acted to reduce the number of neutrons available for breeding purposes. Moreover the fuel assemblies themselves were surrounded by expensive and difficult to fabricate cans and generally necessitated complicated nozzle structures to properly distribute the flow therethrough.